Aluminum vs iron heads, saw no more RPMs, setup?

[caribbean20]

Just ran my new setup with the Dart aluminum heads in my jet. Spun a Berk mag/bronze A/B at 5,000 rpms, tight pump. No increase over my old iron heads. I run no thermostat and water temperature is less than 120* on my gauge. My specs are below. Questions:
1. With the low compression and aluminum heads, anything to be gained by running higher temperature in the block. Easy option would be to run a thermostat system with 160* stat.
2. How much HP do you think I am leaving on the table with the big impeller? I am reluctant to have it cut down unless my package will generate significant more HP past 5,000.
3. I know I can run up to around 10.5:1 compression with the new heads. If I decide to go that route, mill the heads or new pistons (my short block is like new)?
I saw no increase in rpms with the aluminum heads even thought the ports and valves are bigger in the Darts. I am right around my goal on speed, 72 on the GPS in my 20.5' Caribbean. I may just leave it alone, but you know how it is, if there is some more HP just lurking around the corner, I hate to leave it on the table.
Specs
Gen VI 502 block (casting 10237300) and I am replacing my Gen V cast iron (casting 14097088) heads with Dart Pro 1 aluminum heads with the 310cc intake runners and 119 cc chambers (the mild version). Compression is in the range of 9-9.6:1, not sure.
I have a roller cam with 580 lift, 240 duration, Vic Jr. single plane air gap, Holley 850, EMI Thunder, MSD, Berk 12JG w/ plate, A/B mag/bronze, shoe and droop.

[victorfb]

your new heads make actually slightly less compression than your old 088s. you wouldnt/shouldnt see much diifferance in head swap from the 088s to the dart aluminum unless you went with a 110cc chamber. intake runner volume may come into play with some cam choices.(but probably not much) the 088s have a cc of 118 and you say your new aluminum heads have 119cc which was actually an increase of combustable volume. about the only way at this point to maybe increase power level is to change cam timing. if in fact you have a timing set that is adjustable. other than that its my belief that your biggest gain was losing about 90 pounds of weight in the engine compartment.
oh i think the 160 to 180 temp is about right. i wouldnt change much there.

[junkyardhunter]

Spun a Berk mag/bronze A/B at 5,000 rpms, tight pump.
Your rpm seems kinda low for your engine. JPC Berk A/B 5000 rpm = 365 hp
5400-5600 seems about right for your engine combo.

[Sleeper CP]

The large runner heads will not help you at all at that rpm range. The weight savings is a plus but other than that you are not getting any benifit.
If you had received a 1 point bump in compression that would have been a benifit.
Keep in mind at that rpm range it takes roughly 50 HP to add an additional 250 rpm's, so unless you dyno it you'll never see the differance
Sleeper CP
Big Inch Ford Lover

[steelcomp]

An engine is a combination of parts working together to achieve a final goal. If you have a perfect combination and you arbitrarily change one part, you no longer have a perfect combination. If you have an unknown combination, as in your case, you can't just arbitrarily change a part as important as heads and expect an automatic improvement. I don't mean this to sound critical, but you're only lucky you didn't go backwards. When you change something as important as the heads, you need to at the very least have them flowed, and see where you are with the rest of the combination in regards to weather or not all the other parts will takae advantage of the change. Ask yourself if the current cam is going to work in the rpm range you need with the new heads, and the possible change in compression. What exactly are the flow requirements of your engine at the rpm you wish to run? How does the port size compare to the flow requirements? What's the chamber desigh, and will you need to re-evaluate where your optimum timing will be? Are your intake and carb up to the change? Do you have an exhaust system that will tke advantage of the chcange, or will it hurt your desired results? Just some really nbasic questions you should be able to answer before even buying a new set of heads, if you want to know the results ahead of time. -OR- just throw a couple thou at a set, bolt them on, and hope for the best.
Combination, combination, combination.

[victorfb]

i agree. a total combonation of package including drive system is key. IMHO dont touch the impellor untill you have includuded other changes to your package.

[curtis73]

I can't speak intelligently about the jet side of things, but I can share some experience on the engine side.
The layman will tell you that aluminum heads make more power. The truth is, (all things being equal) they don't... in fact they can make a little less. Aluminum with its higher specific heat capacity wicks away combustion heat faster, meaning there is less energy in the actual combustion. While many rodders say that you can run more compression with aluminum heads, the more accurate statement is that you NEED to run more compression to compensate for the reduction in cylinder pressure if you want to maintain the same power.
In the real world, Car Craft and Hot Rod are your friends They have done several real-world tests on aluminum versus iron heads and have repeatedly shown that it makes little difference. They have done tests on heads that are identical castings, just different materials and have shown only 1-2 hp differences with only a head swap.
The real signifigance of aluminum heads is weight savings, and it can really save you some pounds.
As far as your temperature question... typically higher temps reduce power. That is mostly a function of higher intake charge temperatures, but cooler typically makes more power. I would be more concerned with oil temps. Make sure your oil gets up to an appropriate temperature so that it remains healthy. 200-230 is really healthy for oil. Any more and you're pushing it, any less and you're not letting the contaminants burn/evaporate out. Otherwise, actual engine temps only vary HP by 10-15 hp typically, so finding the optimum temperature for power may only get you .5 mph anyway. I would put a higher stress on the health of the engine and its oil than the half click you might gain.
The one caveat to cooler engines is that they have to be warm enough that no choke is required. If they run too cool you start loosing power to the excess fuel puddling and shear associated with cold engines. With most engines the highest power is attained when the intake runners are just warm enough to prevent fuel dropout.

[wet77]

Exactly what I was thinking Curtis73
At least you will save in the weight department with aluminum:devil:

[cfm]

5000rpm is not taking advantage of modern heads with a 240 at .050" cam on a 502.
With 119cc chambers you are around 8.75:1 compression.
With no t-stat and aluminum intake with aluminum heads you probably don't have enough surface temp heat and have some fuel puddling.
Check your plugs to see if your getting enough heat in there. If they don't show enough heat than you know where to go.
The 310 Dart Pro 1's stock are way better than the stockers.
Tune,tune,tune,tune, and tune ! Check plugs for heat 1st, and then for proper A/F mixtures. Try different total timing specs. Assuming you have proper valvesprings and good lifters try bringing rpm's up. If all still doesn't work possibly it's your boat and not the engine.
BTW: can you list your full cam specs or the manufacturer, part # if you don't have the specs ?

[ck7684]

I can't speak intelligently about the jet side of things, but I can share some experience on the engine side.
The layman will tell you that aluminum heads make more power. The truth is, (all things being equal) they don't... in fact they can make a little less. Aluminum with its higher specific heat capacity wicks away combustion heat faster, meaning there is less energy in the actual combustion. While many rodders say that you can run more compression with aluminum heads, the more accurate statement is that you NEED to run more compression to compensate for the reduction in cylinder pressure if you want to maintain the same power.
In the real world, Car Craft and Hot Rod are your friends They have done several real-world tests on aluminum versus iron heads and have repeatedly shown that it makes little difference. They have done tests on heads that are identical castings, just different materials and have shown only 1-2 hp differences with only a head swap.
The real signifigance of aluminum heads is weight savings, and it can really save you some pounds.
As far as your temperature question... typically higher temps reduce power. That is mostly a function of higher intake charge temperatures, but cooler typically makes more power. I would be more concerned with oil temps. Make sure your oil gets up to an appropriate temperature so that it remains healthy. 200-230 is really healthy for oil. Any more and you're pushing it, any less and you're not letting the contaminants burn/evaporate out. Otherwise, actual engine temps only vary HP by 10-15 hp typically, so finding the optimum temperature for power may only get you .5 mph anyway. I would put a higher stress on the health of the engine and its oil than the half click you might gain.
The one caveat to cooler engines is that they have to be warm enough that no choke is required. If they run too cool you start loosing power to the excess fuel puddling and shear associated with cold engines. With most engines the highest power is attained when the intake runners are just warm enough to prevent fuel dropout.
The above is true, just adding my support to it...unless your old heads were seriously choking your engine, new heads alone arent going to give you more RPM. The parts all need to work together as a team...